Cooling system for superconductive or cryogenic structures



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Int. Cl. H015 7/34, 9/06 US. Cl. 12415 12 Claims ABSTRACT OF THEDISCLOSURE A system for cooling superconductive or cryogenic structures.The system includes an enclosure means for holding a liquid refrigerant,and a wick means extends into the enclosure means to engage a liquidrefrigerant therein. This wick means also extends into engagement withan electrically conductive means for conveying the liquid refrigerantthereto for cooling the same, and a passage means is situated adjacentthe wick means to provide an escape path for liquid refrigerant which isat least partly vaporized. The wick means has a mechanical strengthgreat enough to enable it to simultaneously act as a spacer structure,and the wick means may be made of a bundle of cotton or of a bundle oftwisted or braided fibers of metal or glass.

My invention relates to superconductive or cryogenic structures.

In particular, my invention relates to the cooling of such structures.

During the operation of superconductive or cryogenic electricallyconductive coils, cryotrons, or cables, there is during at least part ofthe time heat which must be quickly dissipated. With superconductorssuch heat is present during a change in the current intensity or duringa transition into the normal conducting state, while with cryogenicconductors or with normal conductors there is always heat when thelatter are loaded. Normally a conductive package of electrical currentconductors, such as a coil or a cable composed of a plurality of cablesections, is cooled only at its exterior surface directly by the liquidcoolant in the event that a liquid cooling medium is used. The heatwhich is present in the interior of the conductive package istransported to the exterior surface thereof by heat conduction. Suchheat conduction can be facilitated by the insertion of good heatconductors, such as copper foils. In order to retain the desiredcompactness of the package, however, the inserted heat conductors cannotbe made with a sufficient thickness, so that this type of cooling of thecurrent conductors in the interior of a conductive package is highlyinadequate.

It is, therefore, a primary object of my invention to provide for liquidcooling of electrical current conductors, particularly superconductiveor cryogenic conductors, in such a way that a sufficient cooling will beassured for those locations to which the liquid refrigerant can haveaccess only with difficulty.

In accordance with my invention the electrically conductive means areplaced in engagement with a wick means which engages a liquidrefrigerant in a suitable enclosure means and which by capillary actionconveys the liquid refrigerant by suction to the electrically conductivemeans for cooling the latter. Also, in accordance with my invention,there is situated adjacent the wick means a passage means which providesan escape path for liquid refrigerant which is at least partlyvaporized.

A further object of my invention is to provide a wick structure whichhas a sufliciently great mechanical strength to enable this wickstructure to act at the same time as a v United States Patent spacerstructure. In order to fulfill this latter requirement, the wick meanscan be composed of a bundle of fine glass fibers, metal fibers, or of aporous tape.

The dissipation of heat from the interior of a structure such as a coil,a cryotron, or a cable having multiple cable sections takes place inaccordance with my invention by vaporizing of the liquid refrigeratingmedium which is continuously replenished by capillary action from outerchambers or passages which are filled with liquid refrigerant into theinterior of the structure without relying on gravity or pumps, while thevapor in the interior of the structure can escape through open passages.In the region of the current conductors where the heat is created wicksand passages for the vaporized refrigerating medium alternate with eachother. The wicks are composed, for example, of bundles or tapes, braidedor twisted fibers, made of glass, silk, cotton, and the like, or theymay be composed of fine wires. It is also possible to use tapes composedof a porous mass.

My invention is illustrated by way of example in the accompanyingdrawings which form part of this application and in which:

FIG. 1 is a fragmentary schematic axial section of a superconductive orcryogenic conducting coil having axially arranged wicks;

FIG. 2 is a fragmentary transverse section of the structure of FIG. 1taken along the line IIII in FIG. 1;

FIG. 3 is a fragmentary schematic axial section of the secondary coil ofa cryogenic transformer having radially arranged wicks;

FIG. 4 is a fragmentary transverse section of the structure of FIG. 3taken along the line IVIV in FIG. 3;

FIG. 5 is a fragmentary partly sectional illustration of asuperconductive coil having axially arranged Wicks;

FIG. 6 is a schematic fragmentary axial section of a coil having discwindings and axially arranged wicks;

FIG. 7 is a fragmentary longitudinal section schematically illustratinga superconductive cable having the structure of the invention;

FIG. 8 is a fragmentary schematic transverse section of the structure ofFIG. 7;

FIG. 9 is a schematic longitudinal illustration of a wick-cooledcryotron;

FIG. 10 is a schematic transverse section taken along line X-X of FIG. 9in the direction of the arrows; and

FIG. 11 is a schematic transverse section taken along line XI-XI of FIG.9 in the direction of the arrows.

FIGS. 1 and 2 respectively illustrate different views of a wound coilwhich has no end flanges. The wire 1 of each winding layer is preventedfrom slipping by means of tapes 2 which are inserted between the windinglayers and which surround the latter at their ends. These tapes 2 aremade of a material which has capillary action and which conveys liquidrefrigerant from the ends 3 of the windings into the interior thereof.The tapes 2 are, as is apparent from FIG. 2, circumferentiallydistributed about the windings, so that these tapes 2 define betweenthemselves passages 4 forming a passage means through which the vaporpresent between the winding layers can easily reach the exterior surfaceof the windings. The windings is situated in a heat-insulating housing 5which communicates with tubes 6, only one of which is illustrated inFIG. 1, by means of which liquid refrigerant is supplied to the interiorof the housing 5 and vapor is conducted away from the interior thereof.As a result of the capillary action of the Wick means 2 a pump for therefrigerating medium becomes unnecessary. The interior winding wires arecooled in a faultless manner at every part of the coil.

FIGS. 3 and 4 show in different views sections of a cryogenictransformer having a deeply refrigerated secondary coil 7 for feeding asuperconductive or cryogenic conductive three-phase current cable, thesecondary coil being provided with an unillustrated primary windingwhich is at a normal temperature. The cryogenic conductive secondarycoil is situated within a double-walled housing 8 which contains betweenits walls a heat insulation 9 (superinsulation). The winding is made upof cables 10 of thin wire, these cables being wound in series in thesequence which is numerically indicated in FIG. 3 so that individualwinding packages are provided. Between the cables of each package areWicks 11 and 12 which extend both in the axial direction of the coil aswell as radially with respect thereto. These wicks hold the windings inspaced relation with respect to each other so as to act as spacers. Inaddition, the groups of windings are supported in spaced relation withrespect to each other by spacer elements 13. Outside of the windingcylinder is a cylindrical chamber 14 for the liquid refrigeratingmedium, so that in this way the structure is provided with an enclosuremeans for the refrigerating medium. Of course, the housing 5 of FIG. 1provides an enclosure means for the refrigerating medium of thisembodiment. In both cases the refrigerating medium is a liquid.

In the case of superconductive windings which have continuous shuntingby means of a conductive coating of lacquer, the cooling system of theinvention which provides conveying of the liquid cooling medium by meansof capillary action can be brought about, for example, in the mannershown in FIG. 5. The coil housing 15 is insulated in its interior and isprovided with fins 16 which support the'windings and at the same timedefine free chambers for the liquid helium. In order to achieve acontinuous shunting for the winding, the individual wire layers carry asilver paste 17 which presses into the tapered spaces defined betweenadjoining wires. The adjoining wire layers are separated from each otherby at least one insulating foil 18 and by wicks 19 which arecircumferentially distributed around the winding layers. The transitionfrom one layer to the next is brought about by silver paste 20 or bywoven tapes which are impregnated with silver paste. In this way ashunting of the adjoining layers is achieved.

This winding structure of FIG. 5 is achieved in the following manner.After the first wire winding layer has been made, the silver paste isapplied and after setting of this paste an insulating tape which isalmost as wide as the layer is applied on the latter. This tape consistsof an impermeable insulating foil such as, for example, polyethyleneterephthalate, provided at its inner surface, in a direction transverseto the axis of the wire, with wicks which extend parallel to the coilaxis. Thus, there remains between these wicks small passages throughwhich vapor is withdrawn. At the transition location of the wire fromone layer to the next, the free hollow space is filled with silverpaste. In order to facilitate the Winding it is possible to place atthese transition locations woven tapes which are also impregnated withpaste.

FIG. 6 illustrates a winding which is wound from tapes 21 in the form ofdouble discs 22. The tapes are insulated from each other or areseparated from each other by semi-conductive layers. Between the twocomponents of each double disc there are radially extending wicks 23inserted in a manner similar to the embodiment of FIG. 3. Also, betweenadjoining double discs it is possible to arrange wicks 24. The passagemeans defined between the wicks will in this case also extend radially.At the outside, around the entire disc winding is a free chamber whichforms an enclosure means for the liquid refrigerating medium.

FIGS. 7 and 8 show in different cross sections a superconductive orcryogenic conductive cable for very high current intensities. The cableis composed of a multiplicity of very fine wires 25 which, for example,are insulated from each other by lacquer or by glass silk which is spunaround the individual wires, and these wires are twisted into theindividual cable sections 26. Thicker yarns or fibers 27 are woundaround the individual cable sections,

and these fibers 27 are made of an insulating material and definebetween themselves the passage means 28 through which the outwardlyflowing gas can escape. As is apparent particularly from FIG. 7, theelements 27 are helically wound around the cable sections 26 with theelements 27 on one cable section spaced from those on an adjoining cablesection. In the interior of the cable is a free enclosure 29 for therefrigerating medium, and within the chamber 29 there is a longitudinalflow of the refrigerating fluid from the supply location of the liquidrefrigerant to the discharge location for the vapor, so that thischamber 29 forms not only an enclosure means for the liquid refrigerantbut also a passage means for the escape of vapor. With correspondinginsulation between the supply and return conductors or between the threephases of an alternating current system, all of the conductors can besituated in a concentric or twisted manner within a singleheat-insulating body 30. The penetration of the liquid helium into theinterior of the cable sections can be improved by inserting during themanufacture of the cable, wicks 31 which extend perpendicularly withrespect to the direction in which the conductors extend.

The wick-cooled cryotron which is illustrated in FIGS. 9-11 includes asintered gate conductor 32 and wicks 33 which extend parallel to theelongated gate 32. These wicks consist of tightly twisted round glassfiber bundles which provide a capillary action between the individualglass fibers. The tapered spaces defined between adjoining glass fiberbundles act as gas passages. The gate conductor, wicks, and passages aresurrounded by an insulating tube or enclosure 34 which preventsimpairment of the cooling system by penetration of casting resin intothe interior intermediate spaces during casting of the cryotron into abody of casting resin 35. At the location of the connection between thesintered cryotron and the bundle of hard superconductors 36, the crosssection of the cryotron is widened into a U-shaped configuration, as isapparent from FIG. 11. In the depression which is created in this way,the cables 36 of hard superconductors are inserted and fixed by solder37. As a result of this widening, the distance between the glass fiberbundles 33 is also increased. The helium bath contained in thesuperconductive cable extends into these widened intermediate spaces, sothat the wicks terminate in the helium bath.

I claim:

1. In a system for cooling superconductive or cryogenic structures,enclosure means for holding a liquid refrigerant, electricallyconductive means for conducting an electric current, wick meansextending into said enclosure means to engage a liquid refrigeranttherein and also engaging said electrically conductive means forconveying the liquid refrigerant thereto by capillary action, so as tocool said electrically conductive means, and passage means situatedadjacent said wick means for providing an escape path for liquidrefrigerant which is at least partly vaporized.

2. The combination of claim 1 and wherein said wick means ismechanically strong enough to act as a spacer structure, and said wickmeans coacting with said electrically conductive means to act as aspacer structure therefor.

3. The combination of claim 1 and wherein said wick means includes abundle of cotton 4. The combination of claim 1 and wherein said wickmeans is composed of a bundle of fine fibers consisting of glass.

5. The combination of claim 4 and wherein said fibers are twisted.

6. The combination of claim 4 wherein said fibers are braided.

7. The combination of claim 1 and wherein said wick means is composed ofporous tapes.

8. The combination of claim 1 and wherein said electrically conductivemeans is in the form of a coil having a given axial direction anddistributed in a radal direction 5 about said axial direction, and saidWick means and passage means extending in at least one of saiddirections.

9. The combination of claim 1 and wherein said electrically conductivemeans has the form of a plurality of individual cable sections combinedinto a single cable, and said wick means including a plurality of wicksrespectively wound helically around said cable sections with the wickswhich engage the individual cable sections being spaced from each other.

10. The combination of claim 1 and wherein said electrically conductivemeans includes an elongated cryotron gate, and said wick means includinga plurality of wicks extending longitudinally along said gate in adirection parallel thereto, and said wicks being spaced from each other.

11. The combination of claim 1 and wherein an insulating tube surroundsand encloses said gate, said wicks, and said passage means.

12. The combination of claim 1 and wherein said wick means is composedof a bundle of fine fibers consisting 5 of metal.

References Cited UNITED STATES PATENTS 3,066,499 12/1962 Fisher et a1.l74-15 10 LEWIS H. MYERS, Primary Examiner.

A. T. GRIMLEY, Assistant Examiner.

US. Cl. X.R.

